1. Field of the Invention
The present invention relates to communication networks and, more particularly, to a method and apparatus for interworking Ethernet and MPLS networks.
2. Description of the Related Art
The various network elements on the communication network communicate with each other using predefined sets of rules, referred to herein as protocols. Different protocols are used to govern different aspects of the communication, such as how signals should be formed for transmission between network elements, various aspects of what the protocol data units should look like, how packets should be handled or routed through the network by the network elements, and how information associated with routing information should be exchanged between the network elements.
Ethernet is a well known networking protocol that has been defined by the Institute of Electrical and Electronics Engineers (IEEE) as standard 802.1. Conventionally, Ethernet has been used to implement networks in enterprises such as businesses and campuses, and other technologies have been used to transport network traffic over longer distances. As the Ethernet standards have evolved over time, Ethernet has become more viable as a long distance transport technology as well.
The original Ethernet standard allowed a source address (SA) and Destination Address (DA) to be specified. Over time, several additional fields have been added to allow other values to be designated with respect to a particular Ethernet frame. The original Ethernet frame format specified by IEEE 802.1 includes a source address (C-SA) and a destination address (C-DA). IEEE 802.1Q added a Customer VLAN tag (C-Tag) which includes an Ethertype, TCI information, and customer VLAN ID. IEEE 802.1ad added a provider VLAN tag (S-Tag), which also includes an Ethertype, TCI information, and subscriber VLAN ID. The C-Tag allows the customer to specify a VLAN, while the S-Tag allows the service provider to specify a VLAN on the service provider's network for the frame. These tags also allow the customer and subscriber to specify other aspects which are not relevant to an understanding of the contribution disclosed herein. When a network is implemented using 802.1ad it may be referred to as Q in Q encapsulation or Provider Bridging (PB). A domain implemented using this Ethernet standard will be referred to as a Provider Bridging (PB) domain.
The Ethernet standard has evolved to also allow for a second encapsulation process to take place as specified in IEEE 802.1ah. Specifically, an ingress network element to a service provider's network may encapsulate the original Ethernet frame with an outer MAC header including a destination address on the service provider's network (B-DA), a source address on the service provider's network (B-SA), a VLAN ID (B-VID) and a service instance tag (I-SID). The combination of customer MAC addresses C-SA and C-DA with the I-SID are commonly referred to as the I-Tag. A domain implemented using this Ethernet standard will be referred to as a Provider Backbone Bridging (PBB) domain.
There are also two other Ethernet standards that have been developed or which are in the process of being developed that may be used in one or more of the domains. Specifically, IEEE 802.1Qay specifies a way for the network elements to switch traffic based on the B-DA and B-VID rather than just forwarding the traffic according to the B-DA. The header of the frames forwarded on an Ethernet network established using this technology is not changed, but the manner in which the information is used is changed to allow forwarding to take place in a different manner. A network domain that forward traffic using this forwarding paradigm will be referred to as Provider Backbone Trunking (PBT). In IEEE 802.1Qay, PBT is commonly referred to as Provider Backbone Bridges-Traffic Engineering (PBB-TE). Thus, the term PBT will be used herein to refer to a network implemented according to this standard.
PBB, PB, and the original Ethernet standard use a spanning tree protocol to determine which links should be used to broadcast traffic on the network and which links should be used to forward unicast traffic on the network. To overcome some of the shortcomings of using spanning trees, another Ethernet control plane is in the process of being developed as IEEE 802.1 aq, in which a shortest path routing protocol such as Intermediate System to Intermediate System (IS-IS) or Open Shortest Path First (OSPF) is used in the control plane to establish forwarding paths through the network. Traffic on the domain may then be forwarded based on the B-DA and B-VID in a manner similar to PBT, but from a control perspective a shortest path routing protocol is used instead of a spanning tree to define routes through the network. A domain implemented in this manner will be referred to herein as a Provider Link State Bridging (PLSB) domain. PLSB is described in greater detail in U.S. patent Ser. No. 11/537,775, filed Oct. 2, 2006, entitled “Provider Link State Bridging,” the content of which is hereby incorporated herein by reference. Since PLSB refers to the control plane, it may be used to control forwarding of packets while allowing encapsulation of the packets using PB, PBB, or PBT as described above.
MPLS is another commonly used networking protocol. MPLS specifies a way in which a label switched path may be established through a network. When a packet is received at an MPLS Label Edge Router (LER) the LER will determine the destination LER for the packet, attach a label to the packet, and forward the packet to a first Label Switch Router (LSR) on the path to the destination LER. The LSR will strip the label from the packet, look up the label to determine the next label to be applied to the packet and the next hop for the path, and forward the packet onward to the next hop. This proceeds hop by hop across the network to cause the packet to be forwarded across the Label Switched Path (LSP) through the MPLS network.
The LSP connects a pair of nodes on the MPLS Network. Since more than one customer may need to transmit traffic between the pair of endpoints, it is desirable to allow multiple customers to share one LSP rather than creating a new LSP for each customer. In MPLS, this is accomplished through the use of Pseudowires. Pseudowires allow traffic for different VLANs to be tagged with a service label, so that traffic from multiple customers, VPNs, etc., can use a common LSP and be differentiated by the egress LER. A service that utilizes a pseudowire will be referred to as a Virtual Private Wire Service (VPWS).
In addition to pseudowires, a branching mechanism was developed for MPLS that will allow a given packet that is received at a label switch router (LSR) to be duplicated and passed out of more than one forwarder. A service that utilizes this feature of an MPLS network will be referred to as a Virtual Private LAN Service (VPLS). VPLS uses pseudowires to set up the paths through the network but allows the paths defined by the pseudowires to branch to emulate a Local Area Network (LAN).
VPLS uses the signaling protocol described in draft-ietf-12vpn-signaling-08.txt and IETF RFC 4447 to set up pseudowires. The content of each of these protocols is hereby incorporated herein by reference. RFC 4447 introduces the concept of an Attachment Group Identifier (AGI) that may be conceptualized as a VPN identifier or VLAN identifier. The AGI specifies a logical group of forwarders at the egress node, rather than a particular individual forwarder. When implemented in this manner, an attachment circuit associated with a particular VPLS or pseudowire is constructed to include the Attachment Group Identifier (AGI) that identifies the group of forwarders, and an Attachment Individual Identifier (All) that identifies a particular forwarder within the group.
In operation, the MPLS network will establish label switched paths through the network using a Label Distribution Protocol (LDP). As part of this process, the LDP will allow the Label Edge Routers (LERs) to exchange AGI/AII pairs that will allow the network to setup the dataplane for the pseudowires. This will set up the forwarders at the nodes to cause the packets to be forward in a specified manner. When a frame arrives at the ingress LER, the ingress LER will check the signaled value of AGI/AII pairs with local information and apply a service label as well as a tunnel label. The tunnel label will be used to forward the frame along the LSP through the MPLS network, while the service label will be used by the egress node to obtain the context of the pseudowire at the egress so that the frame may be sent to the correct set of forwarders. The forwarders will then be used to forward the traffic to the correct customerNVPN as the traffic exits the MPLS network. The AGI/AII pairs are thus used in the signaling phase of establishing the VPLS service by the ingress/egress LERs to coordinate how frames should be handled at the egress to cause the frames to be forwarded to the correct customers.
To monitor how a network is operating, such as to perform fault detection, fault isolation, fault confirmation, and other types of fault detection and remediation, an operator may want to send Operation, Administration, and Maintenance (OAM) service frames across the network. Different OAM flows may be used to monitor different aspects or segments of a connection on the network. For example, an OAM flow may be used end-to-end across the network, may be used to monitor the connection within a particular domain, or may be used to monitor other aspects of the connection on the network. A particular OAM flow will be referred to herein as a Management Entity (ME). By monitoring a particular ME the network manager may determine whether connectivity exists across that portion of the network, and if connectivity does not exist, may enable the network manager to isolate the fault on the network. When Ethernet networks and MPLS networks are required to connect together, a network manager may need to be able to define Maintenance Entities across a combined MPLS/Ethernet network
As discussed above, both Ethernet networks and MPLS networks have implemented features that will allow traffic from different VLANs to be identified, and which will also allow traffic associated with particular service instances within a VLAN to be identified. When the networks are interconnected, it would be advantageous to allow interworking to occur, either at the network level or service level, so that particular services may be offered end-to-end across the interconnected network. Additionally, from a management perspective, it would be advantageous to enable OAM Maintenance Entities to be defined to monitor aspects of the MPLS/Ethernet network.